The difference in diameter between the 2 arterioles (wider in, narrower out) means the blood in the capillaries of the glomerulus is under pressure. Blood enters capillaries faster than it leaves, causing the filtering of substances out of the blood.

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What are the three layers that create a barrier between the glomerulus capillaries and lumen of the Bowman's capsule?

The endothelium lining the blood capillaries. The basement membrane of the Bowman's capsule- where most ultrafiltration takes place. The epithelial cells lining the Bowman's capsule- podcytes.

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What is the structure of the capillary endothelium?

There are narrow gaps (pores) between the cells, which allows some of the substances from the blood plasma to pass through.

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What is the structure of the basement membrane?

Fine mesh of collagen fibres and glycoproteins. These prevent large molecules from leaving the blood- including most proteins and red & white blood cells.

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Describe the structure of the podocytes.

They have finger-like projections called major processes, which ensure there are gaps between the cells. Fluid can then pass between these into the lumen of the Bowman's capsule.

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Which substances are filtered out of the blood during ultrafiltration?

Water, amino acids, glucose, urea, mineral ions.

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Which substances will be left in the capillaries of the glomerulus?

Red blood cells, white blood cells, platelets, large proteins. The proteins lower the water potential of the blood, ensuring some of the water stays in.

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What is the name given to the substances filtered into the capsule?

Glomerular filtrate.

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Why is protein in the urine a sign of hypertension?

High blood pressure damages the lining of the glomerulus, meaning larger proteins can fit through, and end up in the urine.

Cytoplasm has lots of mitochondria for ATP production. The opposite membrane is also highly folded to increase surface area and contains Na+/K+ pumps which drive the reabsorption process.

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Describe the process of reabsorption.

Na+/K+ pump in membrane of cells lining the PCT uses ATP to pump Na+ out and K+ in- active transport. Creates a conc. gradient, so Na+ diffuses back in from lumen of PCT via a protein- carries glucose at the same time- facilitated diffusion.

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Describe the process of reabsorption continued.

Conc. of glucose then increases inside PCT cell. Diffuses out of cell, into tissue fluid, then blood. Salts & glucose have been reabsorbed, so conc. of PCT fluid is dilute, meaning water diffuses out into blood. A.a are reabsorbed same way as glucose

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What happens to any small proteins that enter the Bowman's capsule?

They are reabsorbed in the PCT back into the blood by endocytosis.

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What is the role of the loop of Henle?

To create a very low water potential in the tissue fluid surrounding the nephron. This will ensure even more water is reabsorbed into the blood.

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What does the loop of Henle consist of?

The descending limb, which descends into the medulla. And the ascending limb, which ascends back up into the cortex.

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What happens in the descending limb?

1st part is impermeable & brings the filtrate down into medulla region. 2nd part is permeable to water, so it can leave here by osmosis & return to blood capillaries. The filtrate reaching the 'hairpin' end is very concentrated as the water has left.

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What happens in the ascending limb?

1st part permeable to salts- Na+/Cl- diffuse out. Further up, actively pumps out Na+/Cl- -lowers water pot. in tissue fluid around LoH. Causes more water to be drawn out. Filtrate is dilute at top of limb- lost salts. Then flows down DCT.

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Why does the loop of Henle use a counter-current effect?

The two tubes are running parallel and in opposite directions, allowing exchange of substances between the two. Used to create conditions needed for maximum water reabsorption.

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What happens at the distal convoluted tubule?

Active transport is used if needed to adjust the concentration of salts in the fluid. Then flows into the collecting duct.

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What does the collecting duct do?

The fluid has lots of water as many salts have left. Water is drawn out of the fluid in the collecting ducts into the surrounding tissue fluid and back into blood capillaries by osmosis.